This invention relates to a latch needle, particularly for use in knitting machines.
Knitting machine needles are used in great numbers in flat bed knitting machines, as well as circular knitting machines. The latch needles have a needle shank which, at one end, terminates in a hook (needle head). A pivotally supported latch cooperates with the hook and may swing back and forth between two end positions. In one end position the latch lies with its noucat (latch spoon) against the hook tip and thus closes the inner hook space. In its other end position the latch is in a reverse orientation and thus opens the inner hook space.
In some knitting machines it is desired to maintain the needle latch in a stable position of rest in the vicinity of the respective two end positions. Thus, for example, only one staple end position for the latch may be desired which is in the vicinity of the reverse end position and in which the latch is not in contact with the the needle shank. It is an exemplary purpose of such an arrangement that the thread of a loop which closes the latch may glide in the intermediate space between the latch and the needle shank without being impaled by the tip of the latch (latch spoon).
Occasionally, it may also be required that the latch assume a stable position of rest adjacent the closed end position. This is the case, for example, when the latch is guided from its closed position into its reverse, open position by a brush carried by the knitting machine. The brush may better engage the latch if the latter is slightly spaced from the hook. In any event, however, the latch must not have an excessive distance from the hook to securely avoid damaging of the latch. By moving the latch from its closed position into its reverse position, the thread trapping since is opened and thus a thread for forming a loop may be inserted.
Springs are used for setting the stable positions of rest of the latch. For example, U.S. Pat. No. 3,050,968 describes a latch needle having a needle shank, a hook provided at one shank end and a pivotally supported latch disposed adjacent the hook. The latch projects, with the latch shank, into a saw slot which is traversed by a bearing pin. The bearing pin pivotally supports the latch for swinging motion between a closed end position in which the latch engaged the hook end with the latch spoon and a reverse end position in which the inner hook space is open. In the saw slot a flexion spring is positioned which engages the end of the latch shank. The end of the latch shank has a flattened region which serves as an engagement face and which is contacted by a pressing face of the spring. This arrangement determines a stable position of rest of the latch in which the latch spoon is slightly spaced from the hook tip.
It has been found to be very difficult to apply by a flexion spring of the above-outlined type the relatively large resetting force needed for lifting the latch off the hook tip.
Further, latch needles having spring-supported latches are known, such as shown in FIGS. 7 and 8. The latch needle 1 has a needle shank 2 terminating in a hook 3 having a hook tip 4. The hook 3 is adjoined by a shank region in which a latch slot which is synonymously a saw slot 5 is formed. A latch 6 is pivotally supported in the saw slot 5 by a bearing pin 7. A leaf spring 8 positioned in the saw slot 5 has spring ends 11 and 12 which engage respective seats 14 and 10 formed in the saw slot 5. The spring 8 has flexing locations 15 and 16 on either side of the bearing pin 7. The flexing locations 15, 16, as shown in FIG. 7, may contact the reverse side 17 of the latch 6 as shown in FIG. 7 or may contact an inner side 18 of the latch 6 as shown in FIG. 8. Thus, the flexing locations 15, 16 form pressing faces.
In such a basic construction the position of rest of the latch 6 set by the flexion spring 8 is essentially dependent from the positioning of the bearing pin 7 relative to the flexing locations 15 and 16. The smallest tolerances in the making of the spring 8 or the bearing pin 7 substantially affect the position of rest of the latch 6. A tolerance in the position of the bearing pin 7 in the longitudinal direction of the latch needle 1 also results in a significant error in the position of rest of the latch 6. It is a disadvantageous result of these circumstances that in case that latch 6 is in its reverse end position, a thread, during the return motion of the latch needle 1, may be impaled by the latch spoon or, when the latch is in its closed end position, the brushes may not arrive in contact therewith. Therefore, a proper functioning of the latch needle is not ensured.
In addition, a tolerance in the position of the bearing pin 7 between the needle back 9 and the check 19 results in a significant deviation of the resetting forces from their optimal value. If the resetting forces are too small, the latch cannot be moved into its positions of rest, whereas in case the resetting forces are too large, the latch swings beyond the positions of rest and may be damaged. Again, a reliable operation of the latch needle cannot be ensured.
The position of the latch in its respective position of rest and the force with which the latch is moved and retained in such a position of rest affect the quality of the loops of the knit fabric.
It is an object of the invention to provide an improved latch needle of the above-outlined type for obtaining an ameliorated knit fabric.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the latch needle includes a needle shank; a hook formed at one end of the needle shank; a saw slot formed in the needle shank adjacent the hook; and a latch supported in the saw slot for pivotal motion about a pivot axis. The latch has first and second end positions and a position of rest situated between and end positions adjacent one of the end positions. Further, the latch has first and second engagement faces spaced from one another. A spring situated in the saw slot has a first pressing face which is contact with the first engagement face when the latch is in the position of rest and a second pressing face spaced from the first pressing face. The second pressing face is in contact with the second engagement face when the latch is in the end position adjacent the position of rest.
Thus, the latch needle according to the invention has a spring, determining for the needle latch at least one stable position of rest which is different from an end position. Two engagement faces forming part of the latch and two pressing faces forming part of the spring are provided for this purpose. As a result of this arrangement a position of rest for the latch may be set by the cooperation between the first pressing face and the first engagement face and also, the latch may be moved out from its adjoining end position. For example, the latch may be lifted off the hook by the cooperation between the second engagement face and the second pressing face. This has the advantage that lifting the latch off the hook may be effected by means of a relatively large resetting torque, while the setting of the position of rest may occur with a lesser resetting torque. This, on the one hand, ensures a reliable, secure lifting of the latch off the hook and, on the other hand, a loop gliding over the latch may very easily press the latch against the hook. This occurs at least as long as the latch is exposed to a larger counter torque in the vicinity of its end position. Therefore, the latch has a much lesser tendency to expand the loop sliding thereon than in the prior art arrangement of FIGS. 7 and 8 in which a single engagement face and a single pressing face cause the latch to move from its end position into the respective position of rest.
Further, the latch needle according to the invention is significantly less sensitive to manufacturing tolerances than the conventional latch needle shown in FIGS. 7 and 8. The stable portion of rest is set by the first pressing face and the first engagement face; the first engagement face is preferably arranged at the end of the latch shank. The pressing face of the spring extends preferably parallel to the spring length, that is, parallel or at a small acute angle to an imaginary line which connects the two ends of the spring. In this manner the effect of manufacturing tolerances during flexing of the spring or its positioning relative to the latch in the saw slot is substantially suppressed.
In the latch needle according to the invention the pressing and engagement faces for moving the latch out of its end positions are separated from those pressing and engagement faces which serve for maintaining the latch in a position of rest. As a result, the latch may be held in its position of rest with relatively small resetting forces. This prevents the latch from snapping into its stable position of rest with an excessive force and thus with an excessive speed which would likely lead to overshooting its desired position. Such instances which may occur in conventional needles and may lead to a defective loop formation or even to needle or latch damage, are substantially avoided by the latch needle according to the invention.
The latch needle according to the invention is advantageously so configured that the first pressing face and the first engagement face are out of contact with one another when the latch is situated in its end position and further, the second pressing face and the second engagement face are out of contact with one another when the latch is in its position of rest. This measure separates the motion ranges of the latch in which the first or, as the case may be, the second engagement face/pressing face pair is effective. This arrangement allows to set the resetting torques of the latch independently from one another for the respective motion ranges.
Advantageously, the distance of the first engagement face of the latch from the pivotal latch axis is less than such distance of the second engagement face. This results in relatively large but short-stroke resetting torques applied to the second engagement face. Such large resetting torques ensure a particularly reliable lifting of the latch from the hook and, because of their short stroke, they contribute only inappreciably, if at all, to an expansion of the loops.
The first engagement face is preferably so arranged that, together with the pivotal latch axis, it defines a triangle whose angles adjoining the engagement face are acute angles. As a result, each pivotal motion of the latch from its position of rest tensions the spring, whereby the positions of rest in both pivotal directions are set in a stable manner. This too, contributes to an accurate setting of the position of rest of the latch.
In a preferred embodiment of the invention the pivotal range in which the second pressing face is in an operating engagement with the second engagement face (that is, there is an at least linear or spot contact) is smaller than the pivotal range in which the first engagement face (or its shank-side or terminal edge) is in engagement with the first pressing face.
The first engagement face is preferably planar. In the alternative, however, it may be concave or convex. The engagement face functions as a cam face. Configuring the engagement face as a planar surface has the advantage that the desired position of rest may be accurately set.
The latch needle according to the invention may also be so constructed that the latch has two defined, stable positions of rest adjoining its respective end positions. For this purpose third and fourth engagement faces are provided on the latch, and third and fourth pressing faces are provided on the spring. The pressing faces, particularly the first and third pressing faces, may be identical or may at least partially overlap one another, that is, they enclose a common surface region.
It has been found that the dimension of the pressing faces measured in the longitudinal spring direction is expediently at least twice the spring thickness. This ensures a sufficient stability of the desired position of rest.